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  • What is the justification for Python's power operator associating to the right?

    - by Pieter Müller
    I am writing code to parse mathematical expression strings, and noticed that the order in which chained power operators are evaluated in Python differs from the order in Excel. From http://docs.python.org/reference/expressions.html: "Thus, in an unparenthesized sequence of power and unary operators, the operators are evaluated from right to left (this does not constrain the evaluation order for the operands): -1*2 results in -1."* This means that, in Python: 2**2**3 is evaluated as 2**(2**3) = 2**8 = 256 In Excel, it works the other way around: 2^2^3 is evaluated as (2^2)^3 = 4^3 = 64 I now have to choose an implementation for my own parser. The Excel order is easier to implement, as it mirrors the evaluation order of multiplication. I asked some people around the office what their gut feel was for the evaluation of 2^2^3 and got mixed responses. Does anybody know of any good reasons or conciderations in favour of the Python implementation? And if you don't have an answer, please comment with the result you get from gut feel - 64 or 256?

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  • PHP class constant string variable spanning over multiple lines

    - by ebae
    I want to have a string variable for a PHP class, which would be available to all methods. However, this variable is quite long, so I want to separate it into multiple lines. For example, $variable = "line 1" . "line 2" . "line 3"; But above doesn't work. I tried EOD, but EOD is not allowed within class. And when I declare it outside the class, I can't access the variable from within the class. What is the best way?

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  • Are variable length arrays possible with Javascript

    - by Ankur
    I want to make a variable length array in Javascript. Is this possible. A quick google search for "Javascript variable length array" doesn't seem to yield anything, which would be surprising if it were possible to do this. Should I instead have a String that I keep appending to with a separator character instead, or is there a better way to get a varible length array-like variable.

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  • LIKE operator with $variable

    - by skarama
    This is my first question here and I hope it is simple enough to get a quick answer! Basically, I have the following code: $variable = curPageURL(); $query = 'SELECT * FROM `tablename` WHERE `columnname` LIKE '$variable' ; If I echo the $variable, it prints the current page's url( which is a javascript on my page) Ultimately, what I want, is to be able to make a search for which the search-term is the current page's url, with wildcards before and after. I am not sure if this is possible at all, or if I simply have a syntax error, because I get no errors, simply no result! I tried : $query = 'SELECT * FROM `tablename` WHERE `columnname` LIKE '"echo $variable" ' ; But again, I'm probably missing or using a misplaced ' " ; etc. Please tell me what I'm doing wrong!

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  • Redeclared javascript global variable overrides old value in IE

    - by Yousuf Haider
    (creating a separate question after comments on this: http://stackoverflow.com/questions/2634410/javascript-redeclared-global-variable-overrides-old-value) I am creating a globally scoped variable using the square bracket notation and assigning it a value inside an external js file. In another js file I declare a var with the same name as the one I just created above. Note I am not assigning a value. Since this is a redeclaration of the same variable the old value should not be overriden as described here: http://www.w3schools.com/js/js_variables.asp Create 2 javascript files with the following content : Script1 //create global variable with square bracket notation window['y'] = 'old'; Script2 //redeclaration of the same variable var y; if (!y) y = 'new'; alert(y); //shows New instead of Old in IE Include these 2 files in your html file <html> <head></head> <body> <script type="text/javascript" src="my.js"></script> <script type="text/javascript" src="my2.js"></script> </body> </html> Opening this page in Firefox and Chrome alerts 'old' which is the expected behavior. However in IE 8 the page will actually alert 'new' Any ideas on why this happens on IE ?

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  • Bash: Variable substitution in variable name with default value

    - by krissi
    i have the following variables: # config file MYVAR_DEFAULT=123 MYVAR_FOO=456 #MYVAR_BAR unset # program USER_INPUT=FOO TARGET_VAR=<need to be set> If the USER_INPUT is "foo", I want TARGET_VAR to be the value of MYVAR_FOO (TARGET_VAR=456). If USER_INPUT is "bar" I want TARGET_VAR to be set to MYVAR_DEFAULT (123), because MYVAR_BAR is unset. I prefer it to be sh-compatible and as a substitution string. But it might also be bash compatible and/or in a function. I got these snippets: # Default values for variable (sh-compatible) echo ${MYVAR_FOO-$MYVAR_DEFAULT} # Uppercase (bash compatible) echo ${USER_INPUT^^} I would need something like this: TARGET_VAR="${MYVAR_${USER_INPUT^^}-$MYVAR_DEFAULT}" # or somecommand -foo "${MYVAR_${USER_INPUT^^}-$MYVAR_DEFAULT}" This is to switch a bunch of variables between multiple "profiles". In the example, FOO and BAR are profiles. New profiles should be added easily, in this example there would be an implicit profile named BAZ, too, all variables to their default values. Unfortunately it is not that easy. Do you have an idea to solve this? Thanks in advance, krissi

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  • Apache RewriteRule with a RewriteMap variable substitution for the VAL argument to environment variable

    - by Eric
    I have an Apache server that serves up binary files to an application (not a browser). The application making the request wants the HTTP Content-MD5 header in HEX format. The default and only option within Apache is Base64. If I add "ContentDigest on" to my VirtualHost, I get this header in Base64. So I wrote a perl script, md5digesthex.pl, that gives me exactly what I want: MD5 in HEX format but I'm struggling with the RewriteRule to get my server to send the result. Here is my current Rewrite recipe: RewriteEngine on RewriteMap md5inhex prg:/www/download/md5digesthex.pl RewriteCond %{REQUEST_URI} ^/download/(.*) RewriteRule ^(.*) %{REQUEST_URI} [E=HASH:${md5inhex:$1}] Header set Content-MD5 "%{HASH}e" env=HASH The problem is that I can't seem to set the HASH environment variable based on the output of the md5inhex map function. It appears this behavior is not supported and I'm at a lost as to how to formulate this...

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  • How to Use an Environment Variable as an Environment Variable Name

    - by Synetech inc.
    Hi, In my pursuit of a solution to another environment-variable/batch-file related problem, I have once again come across a problem I have visited before (but cannot for the life of me remember how, or even if I solved it). Say you have two BAT files (or one batch file and the command line). How can one pass an environment variable name to the other so that it can read the variable? The following example does not work: A.BAT: @call b.bat path B.BAT: @echo %%1% > A.BAT > %1 > B.BAT path > %1 It is easy enough to pass the environment variable name, but the callee cannot seem to use it. (I don’t remember if or how I dealt with this the last time it came up, but I suspect it required the less-than-ideal use of redirecting temporary BAT files and calling them and such.) Any ideas? Thanks.

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  • Arguments for or against using Try/Catch as logical operators

    - by James P. Wright
    I just discovered some lovely code in our companies app that uses Try-Catch blocks as logical operators. Meaning, "do some code, if that throws this error, do this code, but if that throws this error do this 3rd thing instead". It uses "Finally" as the "else" statement it appears. I know that this is wrong inherently, but before I go picking a fight I was hoping for some well thought out arguments. And hey, if you have arguments FOR the use of Try-Catch in this manner, please do tell. EDIT For any who are wondering, the language is C# and the code in question is about 30+ lines and is looking for specific exceptions, it is not handling ALL exceptions.

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  • Implementing comparision operators via 'tuple' and 'tie', a good idea?

    - by Xeo
    (Note: tuple and tie can be taken from Boost or C++11.) When writing small structs with only two elements, I sometimes tend to choose a std::pair, as all important stuff is already done for that datatype, like operator< for strict-weak-ordering. The downsides though are the pretty much useless variable names. Even if I myself created that typedef, I won't remember 2 days later what first and what second exactly was, especially if they are both of the same type. This gets even worse for more than two members, as nesting pairs pretty much sucks. The other option for that is a tuple, either from Boost or C++11, but that doesn't really look any nicer and clearer. So I go back to writing the structs myself, including any needed comparision operators. Since especially the operator< can be quite cumbersome, I thought of circumventing this whole mess by just relying on the operations defined for tuple: Example of operator<, e.g. for strict-weak-ordering: bool operator<(MyStruct const& lhs, MyStruct const& rhs){ return std::tie(lhs.one_member, lhs.another, lhs.yet_more) < std::tie(rhs.one_member, rhs.another, rhs.yet_more); } (tie makes a tuple of T& references from the passed arguments.) Edit: The suggestion from @DeadMG to privately inherit from tuple isn't a bad one, but it got quite some drawbacks: If the operators are free-standing (possibly friends), I need to inherit publicly With casting, my functions / operators (operator= specifically) can be easily bypassed With the tie solution, I can leave out certain members if they don't matter for the ordering Are there any drawbacks in this implementation that I need to consider?

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  • php claims my defined variable is undefined

    - by tedders
    My php is a little rusty but this is boggling my mind right now. I googled this and read all the stackoverflow questions I could find that looked related, but those all seemed to have legitimate undefined variables in them. That leads me to believe that mine is the same problem, but no amount of staring at the simple bit of code I have reduced this to seems to get me anywhere. Please someone give me my dunce cap and tell me what I did wrong! <?php //test for damn undefined variable error $msgs = ""; function add_msg($msg){ $msgs .= "<div>$msg</div>"; } function print_msgs(){ print $msgs; } add_msg("test"); add_msg("test2"); print_msgs(); ?> This gives me the following, maddening output: Notice: Undefined variable: msgs in C:\wamp\www\fgwl\php-lib\fgwlshared.php on line 7 Notice: Undefined variable: msgs in C:\wamp\www\fgwl\php-lib\fgwlshared.php on line 7 Notice: Undefined variable: msgs in C:\wamp\www\fgwl\php-lib\fgwlshared.php on line 10 Yes, this is supposed to be a shared file, but at the moment I have stripped it down to just what I pasted. Any ideas?

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  • Variable Scoping in a method and its persistence in C++

    - by de costo
    Consider the following public method that adds an integer variable to a vector of ints(private member) in a class in C++. KoolMethod() { int x; x = 10; KoolList.Add(x); } Vector<int>KoolList; But is this a valid addition to a vector ??? Upon calling the method, it creates a local variable. The scope of this local variable ends the moment the execution control leaves the method. And since this local variable is allocated on a stack(on the method call), any member of KoolList points to an invalid memory location in deallocated stack which may or may not contain the expected value of x. Is this an accurate description of above mechanism ?? Is there a need for creating an int in heap storage using "new" operator everytime a value needs to be added to the vector like described below ????: KoolMethod() { int *x = new int(); *x = 10; KoolList.Add(x); } Vector<int*>KoolList;

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  • Apply Button() to an element inside a variable

    - by Ben
    If have a variable data = '<div>... <button id="remember"> ... </button> ...</div>', is it possible to apply the .button(); method to a button inside that variable? I've tried the following: $('#remember', data).button(); but that doesn't work. After that i just do $(data).dialog();, which works. I've come with a workaround and that's to append the variable data to the document, call the .button() and then call the .dialog(), but appending and removing dialog's divs on the document doesn't seems right.

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  • Python TKinter connect variable to entry widget

    - by Sano98
    Hi everyone, I'm trying to associate a variable with a Tkinter entry widget, in a way that: Whenever I change the value (the "content") of the entry, mainly by typing something into it, the variable automatically gets assigned the value of what I've typed. Without me having to push a button "Update value " or something like that first. Whenever the variable gets changed (by some other part of the programm), I want the entry value displayed to be adjusted automatically. I believe that this could work via the textvariable. I read the example on http://effbot.org/tkinterbook/entry.htm, but it is not exactly helping me for what I have in mind. I have a feeling that there is a way of ensuring the first condition with using entry's "validate". Any ideas? Thank you for your input! Sano

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  • VB.Net variable declaration

    - by dcp
    I notice that both of these compile without any compiler warnings or errors, even with Option Strict and Option Explicit both turned on: Dim x As Exception = New Exception("this is a test") Dim y = New Exception("this is another test") My question is, is it more proper to use the first way (see variable x) or the second way (see variable y)? My guess is that VB doesn't need the As clause since the variable is being initialized in place, so the compiler can infer the type. I tend to like the first way as it just "feels" right and is more consistent with other languages like C#, just wondered if there was some good reason for one way over the other. I guess it's really personal choice.

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  • Powershell - Splitting variable into chunks

    - by Andrew
    I have written a query in Powershell interrogating a F5 BIG-IP box through it's iControl API to bring back CPU usage etc. Using this code (see below) I can return the data back into a CSV format which is fine. However the $csvdata variable contains all the data. I need to be able to take this variable and for each line split each column of data into a seperate variable. The output currently looks like this: timestamp,"Utilization" 1276181160,2.3282800000e+00 Any advice would be most welcome $SystemStats = (Get-F5.iControl).SystemStatistics ### Allocate a new Query Object and add the inputs needed $Query = New-Object -TypeName iControl.SystemStatisticsPerformanceStatisticQuery $Query.object_name = $i $Query.start_time = $startTime $Query.end_time = 0 $Query.interval = $interval $Query.maximum_rows = 0 ### Make method call passing in an array of size one with the specified query $ReportData = $SystemStats.get_performance_graph_csv_statistics( (,$Query) ) ### Allocate a new encoder and turn the byte array into a string $ASCII = New-Object -TypeName System.Text.ASCIIEncoding $csvdata = $ASCII.GetString($ReportData[0].statistic_data)

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  • one variable and multiple controllers..

    - by Simon
    I'm working on a web application, using the CAKEPHP framework. Herefor i need to request one variable on multiple pages (all pages have different controllers). it is oubvious that i get a error on several pages, since the variable isn't declared in all the different controllers. Is there a workaround for this? i've already tried the app:: import to import a controller in another controller, but this doens't seem to work (still get a undefined variable error). Thnx for your cooperation! Regards, Simon

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